Add bwp_size and bwp_start fields to CSI_RS PDU struct at NR UE

Add bwp_size and bwp_start fields to struct fapi_nr_dl_config_csirs_pdu_rel15_t, for usage in the UE Fill bwp_size and bwp_start fields with values from BWP. This fixes an issue from MR2142 at csi_rx.c where fapi_nr_dl_config_csirs_pdu_rel15_t is casted directly into nfapi_nr_dl_tti_csi_rs_pdu_rel15_t, resulting in a mismatch in values due to not having the same fields.